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ISSN Online: 2377-424X

ISBN CD: 1-56700-226-9

ISBN Online: 1-56700-225-0

International Heat Transfer Conference 13
August, 13-18, 2006, Sydney, Australia

EFFECT OF HEATED SECTION SPACING ON NATURAL CONVECTION IN A RECTANGULAR ENCLOSURE WITH THREE HEATED SECTIONS ON THE LOWER SURFACE

Get access (open in a dialog) DOI: 10.1615/IHTC13.p6.40
12 pages

摘要

In order to study the development of unsteady, three-dimensional natural convective flows in relatively complex situations, flow in a rectangular enclosure with three separate heated sections on the lower surface has been numerically studied. The enclosure considered has rectangular horizontal lower and upper surfaces and vertical side surfaces. There are three square, symmetrically placed isothermal heated sections on the lower surface, the rest of this surface being adiabatic. The vertical side-walls of the enclosure are kept at a uniform low temperature and the horizontal rectangular upper surface is adiabatic. Attention has been restricted in the present study to an enclosure that has a width that is twice the height of the enclosure and a depth that is equal to the height of the enclosure. In the situation considered, a steady flow exist at low Rayleigh numbers, an unsteady flow develops at higher Rayleigh numbers and then the flow can again becomes steady at still higher Rayleigh numbers. The main aim of the present study was basically to try to determine the conditions under which the unsteady flow develops and ceases and to determine the effect of the flow unsteadiness on the mean heat transfer rate from the heated surfaces. In particular attention has been given to the effect of the heated section spacing on the conditions under which the unsteady flow develops and ceases and the effect of this spacing on the heat transfer rate. It has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated by using the Boussinesq approach. The solution has the following parameters: (i) the Rayleigh number, Ra, (ii) the Prandtl number, Pr, (iii) the dimensionless size, wH, of the square heated sections and (iv) the dimensionless distance between the heated sections on the lower surface, ws. Because of the applications that originally motivated this work (electronic cooling), results have only been obtained for a Prandtl number of 0.7. Results for a wH value of 1/3 are presented here. The main interest in the present study was the effect of ws on the results, values of between 0 and approximately 0.4 having been considered. Results have been obtained for Rayleigh numbers between 103 and 5×105. The results obtained indicate that the dimensionless heated section spacing, ws, has a relatively strong influence on the heat transfer rate and the conditions under which the flow first becomes unsteady.